<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
/*foo()  // 3
function foo(){
    console.log("1");   // 具名
}
foo()  // 3
var foo = function (){
    console.log("2");
}
foo()  // 2
function foo(){
    console.log("3");
}
foo() // 2*/

var a = 3;
var a = 4;

console.log(a);
</script>
</body>
</html>